Field of the Invention
The invention relates in general to a touch display device, and more particularly to a touch display device capable of increasing a touch report rate and an associated control method.
Description of the Related Art
A touch display device is an image display device that includes an input device. The display device may be, for example, a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDD) or an electroluminescent display (ELD). A touch display device allows a user to input an instruction or message by touching or pressing a touch sensor on a screen through a finger or a stylus, while viewing an image displayed on the screen of the display device.
A conventional touch display device is formed by additionally attaching a touch panel including touch sensors on a common display screen without a touch function. Such type of touch display device is generally referred to as an add-on type touch panel. Compared to a common display screen without a touch function, an add-on type touch panel usually suffers from issues of a larger thickness and poorer light transmittance.
To overcome the issues above and to at the same time eliminate the additional manufacturing process of attaching a touch panel, an in-cell touch technology has been developed for a touch display device. For example, an in-cell touch panel directly places touch sensors into a display screen. In other words, when the manufacture of the display screen is complete, the touch sensors are simultaneously formed without involving the additional process of attaching a touch panel.
For an in-cell touch screen, the time for updating data of all pixels thereon is referred to as one display frame period, and is usually defined by a cycle of a vertical synchronization signal. The reciprocal of the display frame period is generally referred to as a frame update rate, or simply frame rate.
In an in-cell touch screen, some electrodes are required to handle dual functions of image display and touch sensing. Therefore, a time-division method is frequently adopted for these electrodes to sometimes control the function of image display and sometimes handle the function of touch sensing. One simplest is approach is that, after the data of all of the pixels is updated once and before the next display frame period begins, touch sensing is performed and a touch report is transmitted. A frequency of generating touch point information is usually referred to as a touch report rate. In a common in-cell touch screen, the touch report rate is equal to the frame rate. For example, if the frame rate is 60 Hz, the touch report rate of the common in-cell touch screen is also 60 Hz.
FIG. 1 shows an LCD panel 10 and an associated control circuit, which together serve as an example of a touch display device. On the LCD panel 10, a gate driver circuit 12, gate lines G1, G2, . . . and GN, and data lines D1, D2, . . . and DM are formed. The LCD panel 10 includes an active region 14, in which a gate line and a data line 14 intersect to control a pixel. A data driving circuit 16 controls the data lines D1, D2, . . . and DM. A timing controller 18 provides a corresponding signal to the gate driver circuit 12 to cause the gate driver circuit 12 to sequentially scan the gate lines G1, G2, . . . and GN. The timing controller 18 also writes a digital signal into a register of the data driving circuit 16 according to an audio/video signal, and converts the digital signal to an analog data signal to drive the data lines D1, D2, . . . and DM.
FIG. 1 further depicts an equivalent circuit in a pixel Cellnm correspondingly controlled by the gate line Gn and the data line Dm. The pixel Cellnm may be a pixel of any of the colors red, green and blue. The gate line Gn may turn on or turn off a thin-film transistor (TFT) TMnm. Through the turned on TFT TMnm, the data driving circuit 16 may store a data voltage Vnm in a capacitor Cnm of the pixel. A difference between a common voltage VCOM on a common electrode and a data voltage Vnm on a data electrode determines a twist level of the liquid crystals between the two electrodes, and thus determines a level of transmittance of light emitted from a backlight source (not shown) through the pixel Cellnm.
FIG. 2 shows an operating timing applied to the touch display device in FIG. 1. The LCD panel 10 operates in a progressive scan mode. The gate lines G1, G2, . . . and GN are scanned for display in a period 20. The gate driver circuit 12 sequentially scan the gate lines G1, G2, . . . and GN. For example, the gate driving circuit 12 first pulls the gate line G1 to a high voltage while keeping the other gate lines at a low voltage. As such, the TFT of all of the pixels connected to the gate line G1 are all turned on. At this point, the data driving circuit 16 may write appropriate data voltages into all of the pixels connected to the gate line G1 through the data lines D1, D2, . . . and DM, respectively. The gate driver circuit 12 then pulls the gate line G1 down to a low voltage, and pulls the gate line G2 to a high voltage, and the data driving circuit 16 writes appropriate data voltages into all of the pixels connected to the gate line G2 through the data lines D1, D2, . . . and DM, respectively. Thus, in the period 20, the data voltages of all of the pixels in FIG. 1 are updated. An entire image formed by all of the pixels in FIG. 1 is commonly referred to as a frame. In other words, one frame is updated in the period 20.
In a period 22, touch detection and report are performed. After one frame is updated in the period 20, touch detection and report may be performed using the data lines D1, D2, . . . and DM or the common electrode in FIG. 1 in the period 22 to provide one touch report.
In periods 24 and 26, the periods 20 and 22 are repeated. It should be noted that, as shown in FIG. 2, the periods 20 and 22 are completed in one frame period TFRAME, and the periods 24 and 26 are completed in a next frame period TFRAME. If the frame rate in FIG. 2 is 60 Hz, the frame period TFRAME in FIG. 2 is 1/60 second, and the touch report rate, the same as the frame rate, is also 60 Hz.
However, to provide a more sensitive and fast touch response, some software system manufacturers demand a touch report rate to be as high as 100 Hz. Therefore, there is a need for a solution for increasing the touch report rate.